A linear model for the pharmacokinetics of azithromycin in healthy volunteers

The pharmacokinetic profile of azithromycin, after oral ingestion of 500 mg, was determined in 10 healthy volunteers. Statistical and biochemical reason seemed to indicate a zero-order absorption of the drug. The disposition of azithromycin was described by a two-compartment model (plasma compartment and extravascular compartment) with elimination from the plasma compartment. The absorption process ends abruptly after a time T = 2.3 +/- 0.49 h, from the administration. The transfer rate constant from the plasma compartment to the extravascular compartment (k12 = 0.12 +/- 0.04 h-1) and the mean residence time of the drug in the extravascular compartment (MRT2 = 43.53 +/- 13.80 h) indicate a rapid and extensive distribution of azithromycin from the serum into the extravascular fluids. The results confirmed the efficacy of a single daily dose of 500 mg per os for clinical use.